The invention relates to the technical field of textile yarn processing machines.
In particular, the invention relates to machines like those comprising a plurality of working positions, particularly arranged in juxtaposition. Each of them has various means suitable for transforming the yarn in one or a plurality of steps, followed by its rewinding or spooling.
As examples, mention can be made of yarn processing machines which combine, on the one hand, means for advancing the yarns and, on the other, means for treating the yarns. The yarn advance means may consist of cylinders cooperating with press rollers, capstans, thread guides or other. The yarn treatment means may be based on a rotation, conferring on the yarns, for example, a twist on themselves or a winding of the yarns on one another.
The principle of this transformation is known, based on the one hand, on a rotation and conferring a torsion of the yarns on themselves or a winding of the yarns around one another, governed by the ratio of the speed of rotation of the spindle to the speed of travel of the yarn and, on the other, on the control of the yarn tension. A method called “single twisting” can be recalled here, which confers on the yarn a torsion on itself per turn of the spindle, while a “two-for-one twisting” method confers on the yarn two-torsions on itself per turn of the spindle.
In many cases, the transformation method also calls for treating several yarns in parallel, and assembling these yarns for subsequent transformation or spooling. Hence this implies an assembly of several transformed yarns on neighboring positions before sending them together to other transformation means and/or before rewinding them together.
According to the invention, it has appeared important to be able to control this assembly.
In known treatment machines, like those defined previously, they may comprise several members designed to advance the yarns, some of them being provided with non-slip driving means, and others, equipped with means optionally allowing slippage. The relative speeds of these members serve to control the tensions in the yarns, to create stretchings, to obtain stress relief or tension slackening. Only the drive speed, without slippage, of the members, serves to guarantee the speed of travel of the yarn and consequently the uniformity of the twisting.
During the assembly of a plurality of yarns, this means that for the assembled yarns to be of perfectly controlled length (for example, identical lengths), it is necessary:                to have at least one common non-slip yarn advance member or perfectly synchronized members;        for the yarns to reach this member with a perfectly controlled tension (for example, equal tensions) from one yarn to the next.        
In yarn cabling or twisting machines, it is perfectly known to a person skilled in the art to provide a drive device designed to lower the yarn tension, for example, in the form of a capstan or a grid type delivery unit, generally known by the name of pre-delivery unit or pre-feeding unit. In the rest of the specification, the member is referred to as the “first feeding means”. In general, this member permits slippage of the yarn and rotates in overspeed with respect to the yarn travel.
The yarn is then fed to a second “feeding” member, generally without slippage, ensuring control of the yarn travel speed. Very often, this second feed is provided by the rewinding system itself.
This ensures that the tensile force resulting from the yarn tension in the upstream processes is essentially absorbed by the first feeding means.
Reference can be made to FIG. 1, which shows, as an indicative and nonlimiting example, a yarn treatment machine having members suitable for producing an assembly of a plurality of yarns, according to the prior art.
This figure shows that the first feeding and yarn travel means (2a, 2b, 2c, 2d) are aligned together and rotated by a common shaft, by means of a drive member (8). The same applies to the feeding and spooling means (3a, 3b, 3c, 3d), which are aligned together and rotated by a common shaft by means of a drive member (5).
These arrangements serve to obtain a perfect synchronism between the positions. However, this configuration leads to tension variations at the outlet of the first feeding means, low in absolute value, but significant in relative value. These tension variations result from the upstream tension dispersions between the positions, added to which are the variations in friction coefficient, geometric tolerances of the components of the feeding system itself. For example, for an upstream tension of between 10 and 12 N, the outlet conditions may vary from one position to another from 0.3 N to 0.6 N.
While such variations do not have any significant impact on the spooling quality when the yarn is spooled individually, the same cannot be said for an assembly of yarns required to meet an equi-length requirement.
In fact, during an assembly, such relative tension variations at the outlet of the first feeding means are incompatible with the requirements to control the length of the assembled yarns, if the assembly is made at this location.
To attempt to solve this problem, according to the prior art, the assembly is prepared upstream of the first feeding member, with the understanding that at this location, even if the absolute dispersion is wider, the relative dispersion is much narrower. As shown in FIG. 1, as a result, the yarn guide means (7a, 7b, 7c, 7d) from their working position to the assembly point (A), are arranged before the first feeding means (2b), which has the following drawbacks:                the various means (7a, 7b, 7c, 7d), and drive member (5) are installed in the immediate vicinity of the upstream yarn treatment unit;        the guide members are subjected to high tensions, generating severe requirements as regards reliability;        the yarn tension, after assembly, is equal to the sum of the tensions of each yarn, so that the feeding and spooling means on the assembled yarns must be dimensioned to withstand this total tension;        the yarns follow a long route with several corners under high tension which, by internal friction on the guide members, causes deterioration and affects the quality of the yarns;        the difficulty, indeed impossibility, of assembling individual yarns having different characteristics (count, yarn type, number or direction of plies, etc.), due to the differences in tension resulting from these differences in characteristics.        